As couples move from whispering sweet nothings to mounting strategic wedding-planning campaigns, their minds and inboxes will be deluged with checklists and countdowns, vendors and venues. But for the most part, their attention will be riveted by the Big Day, not by what comes after.

And why not? Couples understandably want to savor their giddy joy. The sociologist Andrew Cherlin has observed that marriage has become a capstone, rather than a cornerstone, of adult life. Accordingly, weddings have become less of a symbolic expression of a couple’s commitment to a shared future and more of a curated Instagram spectacle of “having arrived.”

The capstone wedding promotes the notion that its flurry of decisions represents a high point of stress and intensity, to be followed by the predictable routines of married life. Not so. I have been treating couples as a therapist for 20 years. I see couples whose unproductive fights over the dishes or in-laws are virtually unchanged, 17 years in. I also see couples whose frozen 17-year marriage begins to thaw once they start saying difficult things that need to be said.

Newly engaged couples do need to plan a wedding, if they want one. Chicken or fish for 150 doesn’t materialize out of thin air. But while they’re thinking about the Big Day, they should also think about how they will cope with disagreement. We’ve made love and marriage into such an ideal that people are afraid to consider, at the outset, just how stressful it can get.

Take money, a perennial source of wedding-related tension and marital strife. Three-quarters of couples pay more than they intended to for their wedding. According to a survey conducted in Britain, of the couples who went into debt paying for their wedding, a quarter of them immediately regret it. Weddings are expansive (and expensive) times, and a discussion of trade-offs can chafe against romantic enthusiasm.

But money decisions never stop being a challenge. I hear couples talk about money by casting one partner as the obstacle — the wife wants a vacation, the husband wants a car — instead of noting that life itself presents obstacles. Financial decisions need to take into account the other person’s thoughts, which are often in conflict with one’s own. Many people are conditioned to avoid talking openly about money, so they simmer in silence.

Once in a restaurant, I overheard a young woman announce to her dinner partner that she had decided to quit her job to plan their wedding. An excruciating silence ensued. Something had to be said, and I was rooting for the man to say it: Why didn’t you talk about it with me? Instead, he remained quiet.

People who study marriage, or work with couples in therapy, as I do, talk about the need for a “we story,” a collaboration between partners about values and goals. But if couples are going to collaborate, they have to figure out how to have a productive conversation. A conversation — as opposed to parallel monologues — involves two people who are making an effort to understand each other. In the grip of strong emotion, productive conversation can be surprisingly hard.

That is why many manuals offer advice for navigating communication traps. They counsel asking your partner whether it is a good time to talk (since couples routinely broach complicated topics on the fly), and striking a balance between empathy and problem-solving. If your partner is an avoider, don’t give up trying to connect. If your partner is an emoter, stay compassionate and firm: “I’ll be able to respond better if you take it down a couple of notches.” In bad moments, we all need these skills.

In our conflict-averse culture we don’t necessarily think of these skills as part of romance. But I’ve seen how the best marriages involve people who can deal with strong negative emotions — and who are cleareyed about how hard it can be. They don’t avoid anger, but they don’t indulge it. They tackle hard issues without shutting down. They apologize for their own bad behavior.

What will matter most in marriage is what’s possible on the other side of love’s first blush: conversations that are rewarding, intimate and real. It’s not that we come together in electric recognition and pure understanding, then fall away from that through conflict. Rather, we come together in a rush of passion, then we achieve love through continuing conversation.

Through that conversation we cultivate the essential emotional attitude in marriage: I can try to understand what you think and feel, without it taking away from my own experience. Your reality doesn’t cancel out mine.

All this may seem an awfully low priority when the to-do list is a mile long and the wedding planner needs an answer now. But in married life, a sense of emotional emergency almost always means it’s time to slow down. Emotions are often inconvenient.

The artist Georgia O’Keeffe said, “Nobody sees a flower — really — it is so small it takes time — we haven’t time — and to see takes time, like to have a friend takes time.” What most people want from marriage is an intimate friend. The key to lasting love is taking time to understand and respond.

A wedding is a one-shot celebration of tying the knot, but marriage is an open-ended practice of disentangling misunderstandings. I wish the newly engaged great happiness. I also wish that in between picking a caterer and a font for the invitations, they pause to think about how they fight, and how they want to talk.

Daphne de Marneffe is the author of the forthcoming book “The Rough Patch: Marriage and the Art of Living Together.”